绘制自由形状并用曲线标记

Question 1

使用是个好主意smooth cycle，但极坐标可能更容易模仿形状。不要绘制圆形，而是将其设为，node这样您就可以绘制到其边界。bend left的选项draw可以制作弯曲的箭头。

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
\draw[dashed, fill=gray!10] plot [smooth cycle, tension=.8] coordinates {(0:2.8)(30:4)(60:3)(100:3.5)(135:3)(205:3.5)(270:1.4)(315:2.8)} ;
\node[draw, dashed, fill=gray!50, circle, minimum size=20mm, label={[label distance=5mm]105:$U$}](C) at (0,0)  {};
\fill (0,0) circle[radius=2pt]  node[above] {$c$};
\draw (C.center) -- node[below] {$r$} (C.0);
\node (B) at (205:2.5){$B_r(x)$};
\draw[->] (B) to[bend left=45] (C.180);
\end{tikzpicture} 

\end{document}

Answer

使用是个好主意smooth cycle，但极坐标可能更容易模仿形状。不要绘制圆形，而是将其设为，node这样您就可以绘制到其边界。bend left的选项draw可以制作弯曲的箭头。

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
\draw[dashed, fill=gray!10] plot [smooth cycle, tension=.8] coordinates {(0:2.8)(30:4)(60:3)(100:3.5)(135:3)(205:3.5)(270:1.4)(315:2.8)} ;
\node[draw, dashed, fill=gray!50, circle, minimum size=20mm, label={[label distance=5mm]105:$U$}](C) at (0,0)  {};
\fill (0,0) circle[radius=2pt]  node[above] {$c$};
\draw (C.center) -- node[below] {$r$} (C.0);
\node (B) at (205:2.5){$B_r(x)$};
\draw[->] (B) to[bend left=45] (C.180);
\end{tikzpicture} 

\end{document}

Question 2

改编

不要\tikz在里面使用tikzpicture
给 B_r 节点命名，(br)以便稍后用于箭头
定义一个\coordinate (c)圆

绘制箭头：

\draw[->] (br) to [out=90, in=160, looseness=1.5] ($(c)+(160:10mm)$);

使用选项fill=lightgray!30为形状着色

代码

\documentclass[border=8mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}[scale=0.7]
    \draw[dashed, fill=lightgray!30] plot [smooth cycle] coordinates {(1,1.5)(3.5,0.9)(4.8,0)(6,1.3)(7.2,2)(7.5,3.5)(6,4)(4,5)(2.6,3.5)(1,3)};
    \node (br) at (2,1.6) {$B_r(x)$};
    \coordinate (c) at (5,2.3);
    \fill[lightgray] (c) circle[radius=10mm] node [text=black, yshift=10mm] {$U$};
    \fill (c) circle[radius=1mm]  node [above, font=\small] {$c$};
    \draw (c) -- node [above, font=\small] {$r$} ++(10mm,0);
    \draw[->] (br) to [out=90, in=160, looseness=1.5] ($(c)+(160:10mm)$);
\end{tikzpicture}
\end{document}

结果

Answer

改编

不要\tikz在里面使用tikzpicture
给 B_r 节点命名，(br)以便稍后用于箭头
定义一个\coordinate (c)圆

绘制箭头：

\draw[->] (br) to [out=90, in=160, looseness=1.5] ($(c)+(160:10mm)$);

使用选项fill=lightgray!30为形状着色

代码

\documentclass[border=8mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}[scale=0.7]
    \draw[dashed, fill=lightgray!30] plot [smooth cycle] coordinates {(1,1.5)(3.5,0.9)(4.8,0)(6,1.3)(7.2,2)(7.5,3.5)(6,4)(4,5)(2.6,3.5)(1,3)};
    \node (br) at (2,1.6) {$B_r(x)$};
    \coordinate (c) at (5,2.3);
    \fill[lightgray] (c) circle[radius=10mm] node [text=black, yshift=10mm] {$U$};
    \fill (c) circle[radius=1mm]  node [above, font=\small] {$c$};
    \draw (c) -- node [above, font=\small] {$r$} ++(10mm,0);
    \draw[->] (br) to [out=90, in=160, looseness=1.5] ($(c)+(160:10mm)$);
\end{tikzpicture}
\end{document}

结果

Question 3

这是一种实现此目的的方法，它可以重用部分代码。

一些评论：

区域 U 比较棘手。我试过了，to[out=..,in=..]但最终代码并不好。所以我分配了新的坐标和tension=1。

我将部分（而非全部）格式语句移至（重构）样式部分。这样，您只需在一个位置进行更改，例如颜色。如果您考虑使用填充图案（这在当今可能不是一个好主意），也可以将它们放在此处。

 \begin{tikzpicture}[
        >={Triangle},%                      arrow tip; try als {Stealth} etc.
        arr/.style={->,line width=1.5pt},%  arrows style
        UF/.style={dashed,fill=gray!20},%   style of U-area
        CF/.style={color=black!60, fill=white!65, very thick},
    ]

箭头做得相当简单，但to[bend left]也可以起到作用：

    \draw[arr] (B) to [out=80,in=140] +(30:2.2);

想像一下之前那里有一条直线；终点是我任意设置的，因为选择的路径使圆不属于节点：

    \draw[arr] (B) -- +(30:2.2);

如果它是节点的形状，您可以使用 (M)、(M.west)、(M.120) 等位置，它将在所述位置结束。

\documentclass[10pt,border=3mm,tikz]{standalone}
%\usepackage{tikz}%             already loaded, see class
\usetikzlibrary{arrows.meta}%   has many nice arrow tips

\begin{document}

 \begin{tikzpicture}[
        >={Triangle},%                      arrow tip; try als {Stealth} etc.
        arr/.style={->,line width=1.5pt},%  arrows style
        UF/.style={dashed,fill=gray!20},%   style of U-area
        CF/.style={color=black!60, fill=white!65, very thick},
    ]
    % ~~~ area U ~~~~~~~~~~~~~~~~~~~
    \draw[UF] plot [smooth cycle,tension=1]
        coordinates {(0.5,.5)(0,2)(1.5,3)(2.5,5)(5,4)(7,3)(6,.5)(4,.5)}
        node at (3,4) {$U$};;
    
    % ~~~ circle ~~~~~~~~~~~
    \coordinate (M) at (4,2);%      saves typing
    \filldraw[CF] (M) circle (1);
    \draw[fill=black,line width=1.2pt] (M) circle (1mm) 
            node [yshift=3mm] {$c$} --
            node[yshift=+2mm,xshift=0mm] {$r$} +(1,0);
            
    % ~~~ B ~~~~~~~~~~~~~~
    \node (B) at (1,1) {$B_r(x)$};
    
    % ~~~ arrow ~~~~~~~~~
    \draw[arr] (B) to [out=80,in=140] +(30:2.2);
 \end{tikzpicture}
\end{document}

PS：这是一个将样式更改为这样的示例：

 \begin{tikzpicture}[
        >={Triangle},%                      arrow tip; try als {Stealth} etc.
        arr/.style={->,line width=1.5pt,blue},% arrows style
        UF/.style={dashed,fill=gray!10},%   style of U-area
        CF/.style={color=black!60, fill=gray!65, very thick},
    ]

Answer